The present invention relates to a technique effectively applied to a high frequency power amplifier for use in a radio telecommunication system such as a portable telephone and for amplifying a high frequency signal and outputting an amplified signal, and to an electric part in which the high frequency power amplifier is assembled. More particularly, the invention relates to a technique for improving power efficiency by reducing distortion in a signal in a region where an output power is low in a radio telecommunication system for detecting an output level necessary for a feedback control of an output power by a current detecting method, sending a feedback signal to each of amplification stages of a high frequency power amplifier having a multi-stage configuration in accordance with the detected output level, and controlling a bias.
Generally, in a transmission part of a radio telecommunication apparatus (mobile telecommunication apparatus) such as a portable telephone, a modulation circuit for modulating a transmission signal and a high frequency power amplifier for amplifying the modulated signal are assembled. In a conventional radio telecommunication apparatus, to control the amplification factor of the high frequency power amplifier in accordance with a requested output level from a baseband circuit or a control circuit such as a microprocessor, the level of an output power of an antenna is detected and is fed back (for example, Japanese Unexamined Patent Application No. 2001-7657). Hitherto, the output power level is generally detected by using a coupler, a detector, or the like.
The high frequency power amplifier in a conventional radio telecommunication apparatus has a configuration in which a plurality of transistors for power amplification are connected in a number of stages (generally, three stages). The amplification factor of the high frequency power amplifier is controlled by, as shown in FIG. 8, applying voltages Vg1, Vg2, and Vg3 obtained by dividing an output control voltage Vapc by resistors R11 to R19 to gate terminals of transistors Q1 to Q3 (base terminals in bipolar transistors) in the amplification stages of the high frequency power amplifier.